Preheat oven to 350 degrees F. Line baking sheet with parchment paper.
In a large bowl, beat on medium speed the butter, eggs, sugar and peppermint extract until combined. In a separate bowl, mix together flour, baking powder and salt. Stir 1/2 of the flour mixture into the egg mixture. Stir in remaining half of flour when first half is fully combined into the butter mixture. Stir in crushed peppermint.
On a floured cutting board, divide dough in half. Shape each dough half into a long roll, approximately 14-16″ long. Carefully place rolls on prepared baking sheet, about 3″ apart from each other. With your hand, press down each roll so that they are approximately 1/2″ high.
Bake for 25 minutes or until golden brown. Carefully remove from pans and place on cooling racks. Set aside baking sheet, as it will be reused. When biscotti had cooled enough to handle, but is still warm, carefully move them to a cutting board and cut crosswise slices (approximately 1/2″ in size). Place slices, cut side down, back on original baking sheet. Bake for 5-10 minutes or until somewhat firm. Transfer to wire racks to completely cool, with tops upwards.
Place white chocolate chips and shortening in a small bowl. Heat for 20 seconds to melt chips. Stir, and if necessary, continue microwave at 5-10 second intervals to completely melt chocolate. Place chocolate in a small zipper-style plastic bag, seal, and snip off a very tiny corner of the bag. Squeeze out white chocolate through this small hole (increase size if necessary) and drizzle back and forth over the tops of the biscotti. While drizzle is still wet, sprinkle with crushed peppermint candies.